This invention relates to an azo polymerization initiator composition and a process for producing the same.
Azo compounds are effective as polymerization initiators for unsaturated vinyl monomers and the like and are widely used. However, azo compounds are disadvantageous in that when stored, they agglomerate into a block during the storage and cannot be used as they are as polymerization initiators. On the other hand, in recent years, polymerization in a closed system has been aimed at, so that azo compounds have been used in the form of a solution in an organic solvent. However the employment of organic solvents involves problems, for example, in recovering the organic solvents after use, and is disadvantageous from the viewpoint of preservation of natural resources and safety and sanitation, and hence is not preferred.
Employment of azo polymerization initiators in the form of an aqueous suspension is preferred because it removes the defects of the above-mentioned method comprising the dissolution in organic solvents. However since azo compounds are insufficiently hydrophilic, the stability of the aqueous suspension becomes a problem when they are merely dispersed into water. In order to meet such a demand, the present inventors have proposed a process for producing an aqueous suspension containing substantially no organic solvent and containing an azo compound in the form of fine particles by dissolving an azo compound in an organic solvent, emulsifying the resulting solution by addition of water, a water-soluble polymer, a surface active agent and the like, and then allowing the organic solvent to evaporate (U.S. patent application Ser. No. 433,690 filed Oct. 12, 1982). According to this process, the aqueous suspension containing the azo compound contains no foam, and hence there can be produced an aqueous suspension which has excellent dispersing stability for a long period of time and permits usual pump transport.
However, this aqueous suspension contains the azo compound in an amount of usually 1 to 50% by weight, preferably 5 to 40% by weight, and water in an amount of usually about 3 to 20 times as much as the azo compound and hence is inconvenient, for example, in that it requires a large space for storage and high energy and much time for transport.